FastAPI admite dependencias que realizan algunos <dfn title='a veces también llamado "código de salida", "código de limpieza", "código de teardown", "código de cierre", "código de salida del context manager", etc.'>pasos adicionales después de finalizar</dfn>.

Para hacer esto, usa `yield` en lugar de `return`, y escribe los pasos adicionales (código) después.

/// tip | Consejo

事實上，FastAPI 內部就是使用這兩個裝飾器。

///

## 使用 `yield` 的資料庫相依 { #a-database-dependency-with-yield }

例如，你可以用它建立一個資料庫 session，並在完成後關閉。

只有 `yield` 之前（含 `yield` 本身）的程式碼會在產生回應之前執行：

{* ../../docs_src/dependencies/tutorial007_py310.py hl[2:4] *}

由 `yield` 產生的值會被注入到路徑操作（path operation）與其他相依中：

{* ../../docs_src/dependencies/tutorial007_py310.py hl[4] *}

位於 `yield` 之後的程式碼會在回應之後執行：

    @Test
    public void testGetKeywordsWithEmptyField() {
        // Test with empty field array
        String query = "test query";
        String[] fields = {};
        List<String> keywords = SuggestUtil.getKeywords(query, fields);
        assertNotNull(keywords);
        assertEquals(0, keywords.size()); // No keywords because no fields match
    }

    @Test
    public void testGetKeywordsWithComplexQuery() {

        String[] fields = { "field" };

        SuggestItem item = new SuggestItem(text, readings, fields, 1L, 1L, 1.0f, new String[] { "tag" }, new String[] { "role" },
                new String[] { "en" }, SuggestItem.Kind.QUERY);

        Map<String, Object> source = SuggestItemSerializer.toSource(item);

        // Verify all expected fields are present

// whitespace characters, as defined by [unicode.IsSpace].
// The iterator yields the same subslices that would be returned by [Fields](s),
// but without constructing a new slice containing the subslices.
func FieldsSeq(s []byte) iter.Seq[[]byte] {
	return func(yield func([]byte) bool) {
		start := -1
		for i := 0; i < len(s); {
			size := 1
			r := rune(s[i])

// JSON utilities with proper escaping
String escaped = JsonUtil.escape("Hello \"World\" with special chars");
String unescaped = JsonUtil.unescape(escaped);

// Text tokenization
Tokenizer tokenizer = new Tokenizer("field1,field2,field3", ",");
while (tokenizer.hasMoreTokens()) {
    String token = tokenizer.nextToken();
    // Process each token
}

// Decimal formatting

        item.setReadings(newReadings);
        assertArrayEquals(newReadings, item.getReadings());

        // Test fields
        String[] fields = { "field1", "field2" };
        item.setFields(fields);
        assertArrayEquals(fields, item.getFields());

        // Test tags
        String[] tags = { "tag1", "tag2" };
        item.setTags(tags);

        QueryBuilder fieldsFilter = request.buildFilterQuery("fields", Arrays.asList("field1"));

        assertTrue("Tags filter should contain 'tags'", tagsFilter.toString().contains("tags"));
        assertTrue("Roles filter should contain 'roles'", rolesFilter.toString().contains("roles"));
        assertTrue("Fields filter should contain 'fields'", fieldsFilter.toString().contains("fields"));
    }

## `ServerSentEvent` { #serversentevent }

If you need to set SSE fields like `event`, `id`, `retry`, or `comment`, you can yield `ServerSentEvent` objects instead of plain data.

Import `ServerSentEvent` from `fastapi.sse`:

{* ../../docs_src/server_sent_events/tutorial002_py310.py hl[4,26] *}

The `data` field is always encoded as JSON. You can pass any value that can be serialized as JSON, including Pydantic models.

        Map<String, Object> source;
        while ((source = reader.read()) != null) {
            assertTrue(source.get("field1").toString().startsWith("test"));
            valueSet.add(source.get("field1").toString());
            count++;
        }
        assertEquals(num, count);
        assertEquals(num, valueSet.size());
    }

    @Test